DESCRIPTION

This set of functions is for tranferring bytes in the relevant transfer mode. For ECP and EPP modes two types of transfer are possible:
data
and
address
(usually referred to as
channel
in ECP).

The supplied
port
must be a claimed port.

The supplied
buffer
must be at least
len
bytes long. When reading, the transferred data is stored in the buffer; when writing the data to be transferred is taken from the buffer.

For reads (peripheral to host): if no data is available and
F1284_NONBLOCK
is not in effect, the inactivity timer is started. If data becomes available before the inactivity time-out elapses it is read; otherwise the return value will be
E1284_TIMEDOUT.

For writes (host to peripheral): if the peripheral is not willing to accept data and
F1284_NONBLOCK
is not in effect, the inactivity timer is started. If the peripheral indicates that it is willing to accept data before the inactivity time-out elapses it is sent; otherwise the return value will be
E1284_TIMEDOUT

The
flags
may alter the behaviour slightly:

F1284_NONBLOCK

For reads (peripheral to host): if no data is available, return immediately (with
E1284_TIMEDOUT).

For writes (host to peripheral): if the peripheral is not willing to accept data, return immediately (with
E1284_TIMEDOUT).

F1284_SWE

Don't use hardware assistance for the transfer, but instead set the parallel port pins according to the wire protocol.

F1284_RLE (for ECP only)

Use run length encoding. If the peripheral is in ECP mode with RLE, calls to
ieee1284_ecp_read_datamust
set this flag in order for the RLE from the peripheral to be interpreted correctly, and calls to
ieee1284_ecp_write_datamay
set this flag in order to take advantage of RLE.

F1284_FASTEPP (for EPP only)

Use multi-byte transfers. Several bytes at a time are transferred using hardware assistance, if supporting hardware is present. The price of this increased speed is that the return value will be less reliable when this flag is used.

For ECP mode, a given direction is in force at any particular time, and it is up to the application to ensure that it is only writing when in forward mode, and reading when in reverse mode.

RETURN VALUE

The return value is the number of bytes successfully transferred or, if negative, one of:

E1284_NOTIMPL

This transfer mode and flags combination is not yet implemented in libieee1284.

E1284_TIMEDOUT

Timed out waiting for peripheral to handshake.

E1284_NOMEM

Not enough memory is available.

E1284_SYS

There was a problem at the operating system level. The global variable
errno
has been set appropriately.

E1284_INVALIDPORT

The
port
parameter is invalid (for instance, perhaps the
port
is not claimed).

If any bytes are successfully transferred, that number is returned. An error is returned only if no bytes are transferred.

For host-to-peripheral transfers, all data is at the peripheral by the time the call returns.